Despite increases in ozone, which suppresses plant growth, pollen production is expected to more than treble in the next 100 ans.

In the study, grass plants were grown in special reactor chambers and exposed to different atmospheric gas concentrations, with different ratios of carbon dioxide and ozone to show their effects on grass and pollen production.

The researchers focused on Timothy grass, which is a major cause of hay fever. Timothy grass extract is used in the oral lyophilisate Grazax, the immunotherapy tablet for hayfever.

They found that an atmospheric CO2 concentrations of 800 parts per million – possible by the end of the century according to some forecasts – raised pollen production per grass flower by 53 pour cent.

Greater plant growth stimulated by the elevated CO2 further increased pollen levels, resulting in an overall boost of up to 202 pour cent. This was despite the dampening effect of higher ozone levels.

Dr Christine Rogers, the US lead scientist from the University of Massachusetts at Amherst said:

‘Stimulation of grass pollen production by elevated CO2 will increase airborne concentrations and increase exposure and suffering in grass pollen-allergic individuals.

‘This is the first evidence that pollen production is significantly stimulated by elevated carbon dioxide in a grass species and has worldwide implications due to the ubiquitous presence of grasses in all biomes (vegetation habitats) and high prevalence of grass pollen allergy.

‘These results are similar to our other studies performed in other highly allergenic taxa such as ragweed but with more extreme outcomes and wider impacts.’

The Research Article: Projected Carbon Dioxide to Increase Grass Pollen and Allergen Exposure Despite Higher Ozone Levels was published on 5th November 2014 in the online journal Public Library of Science ONE.

‘Due to the widespread existence of grasses and their importance in eliciting allergic responses, these results indicate there will be a significant impact on human health worldwide as a result of future climate change.’